High frequency switch power supply technology is widely used in industry, agriculture and national defense currently, especially resistance welding, to reduce the volume of resistance welding machine and save an amount of copper. However, due to electronic devices, materials of high frequency transformer and the limitations of production process, distribution parameters (capacitance, inductance, leakage inductance and loss) of high frequency transformer are increased and high frequency transformer is difficult to output a large current at low voltage, particularly, the duty rate is lower and can not meet the needs of production. The disadvantages said above are mainly reflected in the following four aspects:
First, because the capacitance and inductance are too large and magnetic circuit is too long and the leakage inductance is intense, the expect stress of IGBT is too high.
Second, because the parameters of single transformer and the discreteness of performance, the prior art is difficult to use multiple transformers in parallel.
Third, because multiple power supplies are connected in parallel, taking sharing current technology, responding slowly, high cost, complex circuit, the prior art is difficult to meet the requirements of spot welding machine and the volume is too large.
Fourth, the loss of transformer is too large. The cooling of high frequency transformer is difficult. The duty rate is low.